Electric blasting caps



Dec- 15, 1959 J. J. ONI -IlLL, JR

ELECTRIC BLASTING CAPS Filed Aug. 7, 1957 FIG. 2.

FIG. I.

FIG. 3.

2,916,994 ELECTRIC BLASTING CAPS John J. ONeill, Jr., Alton, Ill assignor to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation or Virginia Application August 7, 1957, Serial No. 676,823

' 5 Claims. 01. 102-28) bridge wire. The bridge wire is thus disposed in the complcted cap so that upon becoming heated, the igniter componcnt of the cap initiates the detonation of the explosive charge In s'ome'cases, the igniter component is formed asabead abo ut the bridge wire while inother cases the bridge wire 'is surrounded by a loose igniter charge.

Electric blasting caps as normally prepared are provided with lead wiresof substantiallength. Such lead wires are provided throughout'their length withaninsulati'n'g sheath to protect the'm fro'm coming in contact with a source of electrical energy that would cause their premature initiation. In addition, the ends of the lead wires are bared and shunted by any suitable means. Such protective measures are quite effective in most instances normally met in the field. However, they are often inadequate when the detonators are used in the proximity of radio frequency energy generators and transmitters. In fact, the lead Wires of electric detonators when in the proper position can serve as antennae which will pick up the radio frequency energy and induce a firing current into the detonator circuit leading to the premature firing of the detonator. The characteristic of detonator lead wires has discouraged their usage in the proximity of radio and radar transmitters. This hazard is also prevalent in connection with television transmitters, microwave relays and loran transmitters.

When it is necessary to use electric blasting caps in areas close to transmitters of radio frequency energy, the problem is particularly acute. This has proved to be a substantial barrier to the utilization of electric blasting caps and other electrically initiated explosive devices in military aircraft and other militaryvehicles equipped with radio, radar and other radio frequency transmitting apparatus. While the eflicacy of electric blasting caps and the like to serve as initiating means for self-destruction of classified material is well recognized, the tendency of their electrical terminals to act as antennae for radio frequency energy has presented a serious hazard in such applications of electric initiators.

It is, therefore, an object of this invention to provide a novel plug-in type detonator protected from accidental discharge by radio frequency energy.

Other objects will become apparent to those skilled in the art when the following description is read in connection with the accompanying drawings.

These objects are accomplished in accordance with this invention, generally stated, by providing a plug-in type electric blasting cap having a metallic shield extending the full length of the conductors in the cap. In

1 United States Patent 0 2,916,994 Patented Dec. 15, 1959 other words, the leg wires are severed as they emerge from the top surface of the bridge plug or are permitted to extend therefrom for only a short distance and a metallic shield positioned about the detonator is substantially co-extensive with the leg wires. Thus, the blasing cap of this invention is provided with short terminals that are particularly adapted for connection to lead wires or to a firing circuit. The terminals may be of the pin or the split sleeve type and in each instance the metallic shield about the blasting cap shields them throughout their entire length from radio frequency energy.

The advantages of this invention can be realized with electric blasting caps having either metal or plastic cases and any type of sealing means. The metallic shield can take the form of a retractable sleeve in slidable engagement with the outside wall of the blasting cap. Alternatively, the shield can be a metallic cap which is fitted ice over the open end of the blasting cap. In any event, the.

metallic shield is at least co-cxtensive with the conductors in the blasting cap and preferably extends slightly beyond the free ends of the conductors and also covers that area of the blasting cap containing the ignition charge.

Three embodiments of this invention are illustrated in the accompanying drawings in which:

Figure 1 is a longitudinal sectional view of an electric blasting cap made in accordance with the present invention;

Figure 2 is a longitudinal sectional view of another embodiment of this invention; and

' Figure 3 is a longitudinal sectional view of an additional embodiment of this invention.

The electric blasting cap shown in Figure l is-providedwith a thermoplastic case 1 having flange 2 about its base and containing a suitable explosive train indicated generally at 3. The mouth of the case is sealed in a conventional manner by plug 4 provided with a pair of conductors 5. The firing circuit of the blasting cap is completed by extending a bridge wire 6 between the internal ends of the conductors 5. The outer ends of the conductors take the form of split sleeve type terminals 7. The blasting cap is also provided with a metallic shielding sleeve 8 which forms a sliding fit with the blasting cap case 1. The sleeve is held in an operative position by helical spring 9 which is attached at one end to flange 2 of the blasting cap case and at the other to extension 10 of the sleeve. In operation, the sleeve can be retracted as the split sleeve type terminals 7 are brought in contact with lead wires or any other type of firing circuit.

Figure 2 illustrates a modified type of protective shield forming another embodiment of this invention. In this embodiment, a small portion of the blasting cap case 1 is bent substantially at right angles to the blasting cap case at its mouth so as to form a tab or sleeve guide 11 cooperating with sleeve guide slot 12. These members cooperate to limit the axial movement of the sleeve 3 and to prevent its separating from the case. Conductors 5 are connected to sleeve type terminals 13 which terminate flush with the upper surface of plug 4.

The electric blasting cap shown in Figure 3 is provided with a thermoplastic case 1 that extends beyond the bridge plug 4 and slightly beyond the exposed ends of the terminals 7. is provided with an inverted metal cup Whose sidewalls 14 frictionally engage the blasting cap case. Here again, it will be noted that the sidewalls 14 of the cup extend below the bridge wire. To make electrical contact with the blasting cap shown in this figure, a plug is used Whose outside diameter is slightly smaller than the inside diameter of the blasting cap case.

It will be understood that the case it may be charged with any suitable explosive mixture including an igniter In addition, the blasting cap' component adjacent the bridge wire 6 which may be either in the form of a bead or in the form of loose composition. 1

Although the term electric blasting cap is used in the specification and claims to describe the invention, it will be understood that this term is used in its broad sense to include electric detonators, squibs, and other types of electrically initiated explosive initiators.

While three complete embodiments of the invention have been disclosed in detail, it is to be understood that the invention is not limited to those embodiments, but on the contrary, that said embodiments are merely illustrative. Accordingly, it is to be distinctly understood that such modifications and variations as present themselves to those skilled in the art without departing from the spirit of this invention are contemplated by and within the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1., An electric blasting cap comprising a case containing an explosive charge, a bridge plug positioned in the case over the explosive charge, the case extending above the top surface of the bridge plug, a pair of conductors carrying a bridge wire, said conductors extending through the plug substantially to the open end of the case, and a metallic cap closed at one end inverted over the open end of the case, the sidewall of the cap extending below the area of the bridge wire.

2. An electric blasting cap comprising a cylindrical case open at one end and closed at the other end, an explosive charge within the case, a flange extending outwardly from the closed end of the case, a bridge plug closing the open end of the case, a pair of conductors carrying a bridge wire, said conductors extending longitudinally through the bridge plug and adapted to be conto the sleeve.

3. An electric blasting cap in accordance with claim 2 in which the conductors end in electrical terminals proximate the top surface of the bridge plug.

4. An electric blasting cap comprising a cylindrical case open at one end and closed at the other end, an explosive charge within the case, a portion of the case at the open end thereof extending outwardly to form a tab, a bridge plug closing the open end of the case, a pair of conductors carrying a bridge wire, said conductors extending longitudinally through the bridge plug and adapted to be connected to lead wires, a metal sleeve in slidable engagement with the cylindrical case, said sleeve being at least coextensive with the conductors, and a longitudinal slot in the sleeve intermediate the ends thereof, said tab being positioned in the slot.

5. An electric blasting cap in accordance with claim 4 in which the conductors end in electrical terminals proximate the top surface of the bridge plug.

References Cited in the file of this patent UNITED STATES PATENTS 991,373 Rennie et al. May 2, 1911 1,912,423 Ayer June 6, 1933 2,093,275 Johnson Sept. 14, 1937 2,393,629 rant Jan. 29, 1946 FOREIGN PATENTS 525,876 Great Britain Sept. 27, 1940 

